It is known that, under particular meteorological conditions, accretions of frost may form on the aerodynamic surfaces of an aircraft in flight, thereby, on the one hand, modifying the aerodynamic profile and hence the aerodynamic characteristics of said surfaces and, on the other hand, making said aircraft heavier and modifying the trim thereof. Such accretions of frost may therefore render the aircraft uncontrollable and cause it to drop.
In order to study the meteorological conditions of frost formation and, thus, anticipate accretions of frost on the aerodynamic surfaces of an aircraft and avoid their consequences, specific campaigns of flight trials are conducted. These trials are aimed at improving the knowledge regarding the shapes of the natural accretions of frost that are apt to be laid down so as to validate already existing models, within the framework of the aircraft certification procedure. Thus, they make it possible to define the shapes of the accretions, to measure the thicknesses and spread thereof in particular about the profile of the aerodynamic surfaces and to determine the state of said profile.
As regards solely the measurement of the thickness of frost accretions, numerous probes are already known which operate by implementing physical principles such as electrical induction and propagation of ultrasounds, microwaves and light beams in frost.
For example, document U.S. Pat. No. 6,425,286 describes an electro-optical probe for detecting frost. This probe comprises a base for fixing it to a surface of the aircraft in contact with the aerodynamic flow, as well as an oblong casing, orthogonal to said base and provided with a cavity in which frost can accumulate. A light beam passes through the cavity and a sensor makes it possible to detect or not the presence of said beam. In case of frost, the latter obstructs the cavity so that the light beam may not be detected by the sensor. This probe furthermore comprises a heating device for melting the frost accumulated in the cavity. By counting the number of heating cycles, the probe can evaluate the total quantity of frost formed.
Regardless of the physical principle on which the operation of these known probes is based, experience shows that they can measure only limited thicknesses of frost and, sometimes, with low accuracy.